Integrated distillation and hydrodesulfurization process for jet fuel production

ABSTRACT

An integrated crude oil distillation and oil hydrotreating process which comprises: A. WITHDRAWING A STRIPPED SIDE CUT FRACTION HAVING A BOILING RANGE BETWEEN 300* AND 700*F. from a stripper in a crude distillation unit at a temperature above 300*F., b. feeding the fraction to a hydrotreating unit before cooling the fraction below 250*F., c. hydrotreating the fraction in a hydrotreater reactor by contacting the fraction with a hydrotreating catalyst and hydrogen at a temperature between 600* and 900*F. and a pressure between 400 and 5000 psig and withdrawing a hydrotreated fraction from the hydrotreater reactor, D. RETURNING THE HYDROTREATED FRACTION TO A SECOND STRIPPER IN THE CRUDE DISTILLATION UNIT BEFORE COOLING THE HYDROTREATED FRACTION BELOW 400*F., e. stripping H2, H2S and light hydrocarbons from the hydrotreated fraction in said second stripper, and F. PASSING THE H2, H2S and light hydrocarbons from the second stripper to the crude oil distillation unit distillation column, thereby utilizing the crude unit overhead system to process the light gases stripped from the hydrotreated fraction. The process of the present invention is economically advantageous compared to processes for jet fuel sweetening by mercaptan oxidation to disulfides.

United States Patent 191 Siegel Dec. 16, 1975 JET FUEL PRODUCTION [75] Inventor: Jack W. Siegel, El Segundo, Calif. [73] Assignee: Chevron Research Company, San Francisco, Calif.

[22] Filed: Feb. 11, 1974 [21] Appl. No.: 441,074

Related US. Application Data [63] Continuation of Ser. No. 194,440, Nov. 1, 1971 abandoned.

[52] US. Cl. 208/211; 208/212; 208/352; 208/354 [51] Int. Cl. C10C 23/00 [58] Field of Search 208/211, 212, 209, 216, 208/347, 350, 354, 355, 352

[56] References Cited UNITED STATES PATENTS 2,998,381 8/1961 Bushnell 208/216 3,310,487 3/1967 Johnson et a1 208/355 3,320,159 5/1967 Potts 208/354 3,356,608 12/1967 Franklin 208/212 Van Pool 208/355 Primary Examiner-Delbert E. Gantz Assistant Examiner-G. .l. Crasanakis Attorney, Agent, or Firm-G. F. Magdeburger; R. H. Davies; D. L. Hagmann OVERHEAD 7 ABSTRACT An integrated crude oil distillation and oil hydrotreating process which comprises:

a. withdrawing a stripped side cut fraction having a boiling range between 300 and 700F. from a distillation unit at a temperature above 300F., b. feeding the fraction to a hydrotreating unit before stripper cooling the fraction below 250F.,

in a crude c. hydrotreating the fraction in a hydrotreater reactor by contacting the fraction with a hydrotreating catalyst and hydrogen at a temperature between 600 and 900F. and a pressure between 400 and 5000 psig and withdrawing a hydrotreated fraction from the hydrotreater reactor,

The process of the present invention is economically advantageous compared to processes for jet fuel sweetening by mercaptan oxidation to disulfides.

3 Claims, 1 Drawing Figure TO GAS PROCESSING couoensea QVERHEAD a neczwmc HYDROTREATER FURNACE NAPHTHA 24 vuoa CRUDE on. NDENSER DISTILLATION K WATER 25 i0 COLUMN J2 2a 2 a I 40 26 FLASH oaum 29 Ha HYDRO- a TREATER SSTEAMI 2 22 REACTOR =3 cauoz OIL as 4; so I J 22 r cauoe OIL STEAM DISTILLATlON uun STRIPPERS E 72 STEAM J6 as I! DIESEL ATMOSPHERIC on.

RESIDUUM TREATED JET INTEGRATED DISTILLATION AND HYDRODESULFURIZATION PROCESS FOR JET FUEL PRODUCTION This is a continuation of application Ser. No. l94,440, filed Nov. 1, l97l, now abandoned.

BACKGROUND OF THE INVENTION The present invention relates to crude oil distillation and hydrodesulfurization of oil.

The heart of essentially all oil refineries is the crude oil distillation unit. In the crude oil distillation unit the crude oil feed to the refinery is heated and then distilled in a crude oil distillation column or atmospheric" distillation column to obtain various boiling range fractions from the crude oil so that the various fractions can efficiently be treated by various refinery methods to obtain the refiners products.

The fractions of the crude oil which are obtained from the crude oil column are often referred to as side cut fractions, as they are withdrawn at various positions along the side of the crude oil distillation or fractionation column. The side cut fractions usually include a kerosene fraction which can be processed or finished to obtain jet fuel. Diesel oil, which is heavier than kerosene, is also withdrawn from the crude oil distillation column as a side product, and is finished so that it may be used as diesel fuel, or is often hydrofined and passed to fluid catalytic cracking so that it can be converted into lighter hydrocarbons suitable for use as gasoline.

The number of side cut fractions from the crude oil distillation column, in many instances, are more than simply a kerosene side cut and a diesel side cut. Excluding a possible naphtha side cut fraction, the side cut fractions usually have boiling ranges within the range of about 300 to 700F., e.g. kerosene, 350-500F.; diesel 500700F. In essentially all cases, the side cut fractions are subjected to stripping in stripper columns to remove light ends from the side cuts before the side cuts are passed to downstream processing. The stripping of the side out removes light ends from the side cuts. The light ends (i.e. light hydrocarbons) removed from the side cuts are passed from the top of the stripper back to the crude oil distillation column.

The side cut strippers for the crude oil distillation column are usually stacked vertically upon one another to conserve space in the refinery, to reduce the cost of foundations, and to conserve on the materials of construction costs. The side cut strippers usually contain only a small number of fractionation trays, for example, about 6 to 12 trays.

In addition to the side cut fractions from the crude oil distillation column, overhead and bottoms fractions are also obtained. The overhead fraction consists at least of an uncondensed gas" fraction and, in many instances, also the liquid overhead product fraction, such as naphtha, is obtained from the overhead system. The gas fraction is treated for recovery of hydrogen sulfide and for separation of the light hydrocarbons into various components, such as an ethane component and an LPG component rich in propane.

An example of a schematic flow diagram for a refinery process scheme including a crude oil distillation unit and various side out processing steps, such as a kerosene hydrotreater and a diesel hydrotreater, is shown on page 62 of Chemical Engineering Progress," May, l967.

US. Pat. No. 3,l85.639 also shows crude oil distillation followed by various downstream processing of side cuts. U.S. Pat. No. 3,356,608 discloses crude oil distillation followed by downstream processing of side cuts from the crude oil distillation unit and also shows the use of separate strippers for the products from the downstream processing. Thus, in US. Pat. No. 3,356,608, a kerosene side cut from the crude oil distillation unit is treated in a light gas oil hydrotreater and the product from the hydro-treater is sent to a stripper in the light gas oil hydrotreating unit.

Combined gas oil desulfurization and naphtha desulfurization are disclosed in US. Pat. Nos. 3,077,048 and 3,172,843. Both of these patents show a hydrotreater product stripper which is not integrated with the crude oil distillation unit.

SUMMARY OF THE INVENTION According to the present invention an integrated crude oil distillation and oil hydrotreating process is provided, which process comprises (a) withdrawing a side cut fraction having a boiling range between 300 and 700F. from a crude distillation unit at a temperature above 300F., (b) feeding the fraction to a hydrotreating unit before cooling the fraction below 250F., (c) hydrotreating the fraction in a hydrotreater reactor by contacting the fraction with a hydrotreating catalyst and hydrogen at a temperature between 600 and 900F. and a pressure between 400 and 5000 psig and withdrawing a hydrotreated fraction from the hydrotreater reactor, (d) returning the hydrotreated fraction to a stripper in the crude distillation unit before cooling the hydrotreated fraction below 400F., (e) stripping H H 8 and light hydrocarbons from the hydrotreated fraction in said stripper, and (f) passing the H H 8 and light hydrocarbon from the stripper to the crude oil distillation unit distillation column, thereby utilizing the crude unit overhead system to process the light gases stripped from the hydrotreated fraction.

The process of the present invention provides an unexpectedly economically attractive process for converting crude oil side cut fractions, such as jet fuel, to jet fuel of reduced sulfur content and, hence, reduced pollution forming tendencies because the hydrotreated jet fuel forms less SO, upon combustion.

The process of the present invention is an economically attractive alternate to jet fuel sweetening by mercaptan oxidation to disulfides, such as in the Merox process; and, of course, the present invention also removes the sulfur compounds rather than simply converting the sulfur compounds to another organic form, such as disulfides.

Advantages of the present invention include the following:

a. Heat is conserved because the side cut fraction is withdrawn hot from the crude oil distillation column and passed before complete cooling to the hydrotreater. Furthermore, the hot product from the hydrotreater is returned to a stripper in the crude oil distillation unit before complete cooling of the hydrotreater product to ambient temperature.

b. Product storage is eliminated for the side cut fraction in between the crude oil distillation unit and the hydrotreating unit.

c. The same stripper foundation, etc. is used for the crude oil unit strippers and for the stripper used to strip the hydrotreating unit product.

d. The overhead system for a stripper which normally would be built as a separate set of equipment for the hydrotreating unit is eliminated. Instead, the overhead from the hydrotreater product stripper is processed in the crude unit overhead system.

According to a particularly preferred embodiment of the process of the present invention, the hydrotreating reactor effluent is cooled from a temperature above 600F. to a temperature below SF., then the pressure on the effluent is reduced by at least 100 psi and introduced to a flash drum, and vapors from the flash drum are cooled and the condensate is combined with hot (400F. or higher) liquid oil from the flash drum and passed to said second stripper.

It is particularly preferred to employ the process of the present invention for jet fuel sweetening. A typical jet fuel fraction boils between about 300 and 600F., for example, between about 340 and 520F. Generally, it is necessary to at least convert the mercaptans in the jet fuel product to disulfides as the mercaptans are undesirable in the jet fuel product for reasons including their foul odors. The hydrotreating processes for the present invention can be readily carried out at conditions sufficient to sweeten the jet fuel fraction by removing the majority of the mercaptans, usually reducing the mercaptans by about 90 weight percent or more. More difficultly removed organic sulfide compounds, such as thiophenes, are often left after mild hydrotreating conditions sufficient to remove the mercaptans. Conditions sufficient to remove the mercaptans include a temperature between 600 and 900F., a pressure between about 400 and 5000 psig, a hydrogen rate of about 100 or 10,000 scf/bbl of oil fed to the hydrotreating reactor. Catalysts used in the hydrotreating step of the present invention can be selected from various known hydrotreating catalysts, such as cobaltmolybdenum, or nickel-molybdenum, or nickel-tungsten catalysts. Usually the catalysts are supported on a refractory support material such as alumina or silicaalumina.

The cobalt and molybdenum components (or, in general, the Group VI or Group VIII metal components) of the catalyst are usually in the fonn of oxides and/or sulfides. The liquid hourly space velocity for the oil through the catalyst is usually between about 0.1 and I0.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a schematic process flow diagram illustrating a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWING AND EXAMPLE Referring now more particularly to the drawing, crude oil, for example, 55,000 bbls per operating clay of Arabian crude oil, is fed via line I to crude oil distillation column line 2. The crude oil is fractionated according to well known processes into various side cut fractions and an overhead fraction and a bottoms fraction as shown in the drawing. The side cut kerosene fraction is withdrawn via line 3, and the side cut diesel fraction is withdrawn via line 4. The overhead is withdrawn via line 5, cooled and condensed in overhead condenser 6, and then passed via line 7 to overhead receiving vessel 8. Reflux is returned to the crude oil distillation column from the overhead receiving vessel 4 via line 9. Naphtha overhead product is withdrawn via line 10.

The bottoms product or atmospheric residuum is withdrawn from the distillation column via line 11. The diesel oil side cut fraction is withdrawn from the crude oil distillation column via line 4, and passed to crude oil distillation unit stripper 12. In particular, the diesel oil side cut fraction is passed to stripper 13. Steam is introduced via line 14 to the bottom of stripper l3, and light hydrocarbons are stripped from the diesel oil fraction as it flows downward from stripper 13. The stripped diesel oil fraction is withdrawn via line 14. The light hydrocarbons stripped from the diesel oil fraction and steam are returned to the crude oil column via line 16. The steam is ultimately removed from the crude oil distillation unit via line 17 after being condensed out of the overhead as water in overhead condenser 6.

In the process of the present invention the side cut fraction fed to the hydrotreating unit from the crude oil distillation unit can be sent directly to the hydrotreater via line 40 without preliminary stripping. This is advantageous in that one less stripping vessel is necessary, i.e. stripper 18 can be eliminated. However, usually the feed to the hydrotreater is stripped to reduce the amount of light ends that are processed through the hydrotreating unit.

Thus as shown in the drawing, a kerosene side cut fraction is passed via line 3 from the crude oil distillation column to stripper 18 at a temperature of about 425F. Steam introduced via line 19 to the bottom of stripper l8 strips light ends out of the kerosene side cut fraction as the kerosene fraction flows downward in the stripper. The light ends and steam are returned to the crude oil distillate column via line 20. The stripped kerosene fraction is passed via line 21 to the hydrotreating unit.

About 8,000 barrels per operating day of stripped kerosene at a temperature of 425F. is combined with about 4 million scf/d of hydrogen-rich off gas from a catalytic reformer as indicated by line 22. The combined hydrogen and kerosene are passed via line 23 to furnace 24. About 30 million btu/hr are added to the combined feed via furnace 24, and then the combined feed is passed via line 25 at a temperature of about 700F. to hydrotreating reactor 26.

The catalyst used in the hydrotreating reactor can be selected from various hydrotreating catalysts as, for example, a hydrotreating catalyst comprising nickel sulfide-molybdenum sulfide on a silica-alumina supl1. Suitable pressure for the reaction directed to removal of mercaptans from the kerosene or jet fuel fraction is between about 400 and 1000 psig, for example, about 600 psig. After the exothermic hydrodesulfurization reaction in reactor 26, the effluent is withdrawn from the reactor via line 27 at a temperature of about 725 T.

In the simplified flow diagram the hydrotreater effluent is shown as passed to only one separator vessel, i.e., flash drum 29, after cooling in exchanger 28. In certain instances two separating vessels can be used instead of one separating vessel. In any case, in the process of the present invention the amount of heat removed from the hydrotreater reactor effluent is not as complete, i.e., not to as low a temperature, as in many hydroconversion units. Thus, instead of cooling the reactor effluent down to about 150 or F. as could easily be done with air exchangers or with the use of water-cooled exchangers, the effluent is cooled only to a temperature of about 400F. In the schematic process flow diagram the effluent is passed via line 30 to flash drum 29 at a temperature of about 425F. and a pressure of about 150 psig. Overhead gases and vapors from the flash drum are passed via line 31 to vapor condenser 32. Vapor condenser 32 serves to condense hydrocarbons by lowering the temperature of the gaseous vaporous stream to about 120F.

About 3.8 million scf/d of hydrogen-rich gas containing H 5 are removed from vapor condenser 32 via line 34 for treatment in an H 8 removal plant. The great majority of the effluent from the hydrotreater reactor is removed from the bottom of the flash drum as a liquid via line 33. Thus, only about 270 barrels per day of oil are removed from vapor condenser 32 via line 35 for combining with about 7,730 barrels per day of oil withdrawn from flash drum 29 via line 33. The combined streams totaling about 8,000 barrels per day are passed via line 36 at a temperature of about 420F. to the crude oil distillation unit stripper 12.

In particular, the hot hydrotreated jet fuel fraction is passed via line 36 to stn'pper 37. The hydrotreated jet fuel contains some dissolved H 5 that does not flash off from flash drum 29 as well as some dissolved hydrogen and some light hydrocarbons, such as methane, ethane, propane and butane, and heavier hydrocarbons that boil below the lower cut point for the jet fuel product. The majority of these light components are stripped out in stripper 37 and passed via line 40 to the crude oil distillation column. The light components are then processed by the crude oil distillation column overhead systems as indicated in the drawing.

The hydrotreated fraction is withdrawn via line 39 from stripper 37 as stripped. treated jet fuel of reduced sulfur. The hydrotreated jet fuel contains only trace amounts of mercaptans, for example, less than about 20, and usually less than about parts per million by weight of mercaptan compounds.

Although the various embodiments of the invention have been described, it is to be understood that they are meant to be illustrative only and not limiting. Certain features may be changed without departing from the spirit or scope of the present invention. It is apparent that the present invention has broad application to integrated crude unit and side cut hydrotreating operation wherein one of the strippers in the crude unit set of strippers is used as the stripper for the hydrotreated product. Accordingly, the invention is not to be construed as limited to the specific embodiments or examples discussed but only as defined in the appended claims or substantial equivalents of the claims.

What is claimed is:

1. An integrated crude oil distillation and oil hydrodesulfurizing process for jet fuel production which comprises:

a. withdrawing a stripped side cut fraction having a boiling range between 300F. and 700F. from a first stripper in a crude distillation unit at a temperature above 300F., said unit including a crude oil distillation column having an associated overhead system, said system comprising an overhead condenser and an overhead receiving vessel,

b. feeding the withdrawn fraction from said first stripper to a hydrodesulfurizing reactor before cooling said fraction below 250F.,

c. hydrodesulfurizing said fraction in said hydrodesulfurizer reactor by contacting the fraction with a hydrodesulfurizing catalyst and hydrogen at a temperature between 600 and 900F. and a pres sure between 400 and 5,000 psig and withdrawing a hydrodesulfurized reaction effuent from the reactor, said contacting being sufficient to sweeten the jet fuel fraction by removing mercaptans,

d. passing the hydrodesulfurized liquid phase separated from step (c) to a second stripper in the crude distillation unit before cooling said liquid phase below 400F.,

e. stripping H H 8 and light hydrocarbons from said liquid phase in said second stripper, said light hydrocarbons boiling below the lower cut point of said side out fraction,

f. passing a stream comprising said H H 8 and light hydrocarbons from said second stripper to an upper portion of said distillation column, and separating normally liquid hydrocarbon components in said stream from said overhead receiving vessel, and

g. withdrawing from said second stripper said hyd rodesulfurized jet fuel poroduct.

2. A process in accordance with claim 1 wherein said hydrodesulfurized reaction effluent prior to being passed to said second stripper is cooled from a temperature above 600F. to a temperature below 500F., is depressured by at least psi and introduced into a flash drum, and wherein vapors from the flash drum are cooled, condensed and combined with the liquid phase from the flash drum, said liquid phase having a temperature of at least 400F., and wherein the resulting liquid phase is passed to said second stripper.

3. A process in accordance with claim 1 wherein said side cut fraction boils in the range between 300 and 600F. 

1. AN INTEGRATED CRUDE OIL DISTILLATION AND OIL HYDRO-DESULFURIZING PROCESS FOR JET FUEL PRODUCTION WHICH COMPRISES: A. WITHDRAWING A STRIPPED SIDE CUT FRACTION HAVING A BOILING RANGE BETWEEN 300*F, AND 700*F. FROM A FIRST STRIPPER IN A CRUDE DISTILLATION UNIT AT A TEMPERATURE ABOVE 300*F., SAID UNIT INCLUDING A CRUDE OIL DISTILLATION COLUMN HAVING AN-ASSOCIATED OVERHEAD SYSTEM, SAID SYSTEM COMPRISING AN OVERHEAD CONDENSER AND AN OVERHEAD RECEIVING VESSEL, B. FEEDING THE WITHDRAWN FRACTION FROM SAID FIRST STRIPPER TO A HYDRODESULFURIZING REACTOR BEFORE COOLING SAID FRACTION BELOW 250*F., C. HYDROESULFURIZING SAID FRACTION IN SAID HYDROESULFURIZER REACTOR BY CONTACTING THE FRACTION WITH A HYDRODESULFURIZING CATALYST AND HYDROGEN AT A TEMPERATURE BETWEEN 600 AND 900*F. AND A PRESSURE BETWEEN 400 AND 5,000 PSIG AND WITHDRAWING A HYDRODESULFURIZED REACTION EFFUENT FROM THE REACTOR, SAID CONTACTING BEING SUFFICIENT TO SWEETEN THE JET FUEL FRACTION BY REMOVING MERCAPTANS, D. PASSING THE HYDRODESULFURIZED LIQUID PHASE SEPARATED FROM STEP (C) TO A SECOND STRIPPER IN THE CRUDE DISTILLATION UNIT BEFORE COOLING SAID LIQUID PHASE BELOW 400*F., E. STRIPPING H2, H2S AND LIGHT HYDROCARBONS FROM SAID LIQUID PHASE IN SAID SECOND STRIPPER, SAID LIGHT HYDROCARBON BOILING BELOW THE LOWER CUT POINT OF SAID SIDE CUT FRACTION, F. PASSING A STREAM COMPRISING SAID H2, H2S AND LIGHT HYDROCARBONS FROM SAID SECOND STRIPPER TO AN UPPER PORTION OF SAID DISTILLATION COLUMN, AND SEPARATING NORMALLY LIQUID HYDROCARBON COMPONENTS IN SAID STREAM FROM SAID OVERHEAD RECEIVING VESSEL, AND G. WITHDRAWING FROM SAID SECOND STRIPPER SAID HYDRODESULFURIZED JET FUEL PORODUCT.
 2. A process in accordance with claim 1 wherein said hydrodesulfurized reaction effluent prior to being passed to said second stripper is cooled from a temperature above 600*F. to a temperature below 500*F., is depressured by at least 100 psi and introduced into a flash drum, and wherein vapors from the flash drum are cooled, condensed and combined with the liquid phase from the flash drum, said liquid phase having a temperature of at least 400*F., and wherein the resulting liquid phase is passed to said second stripper.
 3. A process in accordance with claim 1 wherein said side cut fraction boils in the range between 300* and 600*F. 